Probes of the type used in measuring instruments are known. A desirable type of probe has a mechanism for retracting the probe when not in use. Known mechanisms include a rail and carriage assembly having a probe mounting block attached to the carriage. The mounting block is carried by the carriage and travels along the rail, often driven by a lead screw which is in turn driven by a motor.
Probes of the type with which this invention is concerned are normally either fully retracted or fully extended in use. Intermediate positions are not normally used.
A known actuator is shown in U.S. Pat. No. 6,084,326. In this known mechanism, a lead screw is driven by a motor. When the lead screw is rotated, a displacement member such as a lead screw nut coupled to the screw moves longitudinally. A plurality of magnets couples the displacement member to a carriage having a like plurality of magnets arranged around its inner circumference, and the carriage moves with the lead screw nut.
Known mechanisms of the type described have been widely used but have a few disadvantages. Because of the magnetic coupling, the slider or carriage and probe may be temporarily displaced in a longitudinal direction with respect to the displacement mechanism and disengaged. A rotational displacement and disengagement have not heretofore been possible, however. Furthermore, while known devices are reasonably accurate at the end of travel, they rely on the accuracy of the lead screw threads, the absence of contaminants, and the like for repeatable positioning at the end of travel.
It is an object of this invention to overcome these and other disadvantages of known actuators.